The present invention relates to combustion turbine engines, and more particularly, to fuel injectors disposed downstream of primary fuel nozzles in the combustion systems.
Multiple designs exist for staged combustion in combustion turbine engines, but most are complicated assemblies consisting of a plurality of tubing and interfaces. One kind of staged combustion used in combustion turbine engines is often referred to as “late lean injection.” In this type of staged combustion, late lean fuel injectors are located downstream of the primary fuel nozzle. As one of ordinary skill in the art will appreciate, combusting a fuel/air mixture at this downstream location may be used to improve NOx performance. NOx, or oxides of nitrogen, is one of the primary undesirable air polluting emissions produced by combustion turbine engines that burn conventional hydrocarbon fuels. The late lean injection may also function as an air bypass, which may be used to improve carbon monoxide or CO emissions during “turn down” or low load operation. It will be appreciated that late lean injection systems may provide other operational benefits.
Conventional late lean injection assemblies are expensive and costly for both new gas turbine units and retrofits of existing units. One of the reasons for this is the complexity of conventional late lean injection systems, particularly those systems associated with the fuel and air delivery. The many parts associated with these complex systems must be designed to withstand the extreme thermal and mechanical loads of the turbine environment, which significantly increases manufacturing and installation cost. Even so, conventional late lean injection assemblies still have a high risk for fuel leakage into the compressor discharge casing, which can result in auto-ignition and a safety issue.
Additionally, conventional late lean injectors perform poorly in regard to providing a well-mixed fuel/air mixture for combustion within the combustion chamber. Further, conventional designs fail to efficiently use air supplied from within the flow annulus formed of the combustor.
As a result, there is a need for improved late lean injection systems and components, particularly those that reduce system complexity, assembly time, and manufacturing cost, while also performing effectively and making efficient usage of the air supply flowing through this region of the turbine. Additionally, such injection systems should restrict the back-flow of fluid within the passage that traverses the flow annulus within the combustor so to limit the occurrence of flame-holding.